Extraction process utilizing aqueous arylated carbohydrates as solvents



United States Patent EXTRACTION PROCESS UTILIZING AQUEOUS ARYLATED CARBOHYDRATES AS SOLVENTS George L. Hervert, Downers Grove, and Carl B. Linn, Riverside, 111., assignors to Universal Oil Products Company, Des Plaines, Ill., acorporation of Delaware No Drawing. Application December 31, 1954, Serial No. 479,222

Claims. (Cl. 260-674) This invention relates to a process for separating and recovering aromatic hydrocarbons from hydrocarbon mixturescontaining the same utilizing an aqueous solution of an arylated carbohydrate as the solvent extractant. More specifically, this invention concerns a process for recovering aromatic hydrocarbons from mixtures of the same with other types and classes of hydrocarbons by contacting the hydrocarbon mixture with an aqueous solution of an arylated carbohydrate, particularly an aqueous solution of a mono-arylated hexose sugar containing from about 0.5 to about 20% by weight of said arylated carbohydrate.

This invention is directed to the discovery that the solubility ofaromatic hydrocarbons in water may be substantially increased by dissolving in the water a carbohydrate condensation product of an aromatic compound at suitable conditions of temperature, solvent to feed stock ratio and concentration of arylated carbohydrate in the aqueous solution. The process is particularly directed to a method of separating aromatic hydrocarbons from hydrocarbon mixtures utilizing an aqueous solution containing at least 0.5% up to about 30% by weight of the arylated carbohydrate as a solvent extractant. It has been generally known that aromatic hydrocarbons are soluble to a limited extent in water at elevated temperatures and it is particularly significant that such solubility of the aromatic hydrocarbon series may be increased from 1 to 400% at corresponding temperatures by dissolving in the aqueous solvent an arylated carbohydrate in the amount of from 1 to 10% by weight of the solvent composition. It is furthermore noteworthy that the selectivity of such a resulting solvent for aromatic hydrocarbons over other classes of hydrocarbons is extremely high in spite of the large increase of the solubility of such hydrocarbons in the aqueous solution.

It is therefore one object of this invention to provide a solvent which is highly selective for aromatic hydro,-

carbons when the aromatic hydrocarbon is present in admixture with other classes of hydrocarbon mixtures. Another object of the invention is to provide a process for separating aromatic hydrocarbons from other hydrocarbons in admixture therewith by a method in which the aromatic extract may be readily recovered from the rich solvent phase without excessive consumption of heat or other utilities and in a form unmodified from the hydrocarbon originally present in the feed stock mixture. Still another object of the invention is to provide a process for separating aromatic hydrocarbons from hydrocarbons and mixtures therewith, utilizing a selectivesolvent for the aromatic hydrocarbon component of the mixture which may be continuously recycled in the separation stage without deterioration of the solvent composition.

In one of its embodiments this invention relates to a method of separating an aromatic hydrocarbon from a hydrocarbon mixture containing the same which comprises contacting said hydrocarbon mixture with a solvent composition consisting essentially of an aqueous solution of an arylated carbohydrate to form a rich solvent phase 2,810,003 Patented Oct. 15, 1957 ICQ . 2 comprising said aromatic hydrocarbon dissolved in said aqueous solvent and a rafiinate phase separate from said rich solvent phase comprising the non-aromatic components of said hydrocarbon mixture, separating'said rich solvent from said rafiinate, thereafter removing dissolved aromatic hydrocarbon from said rich solvent.

In its more specific embodiments the present invention relates to the above process effected at temperatures of from about 100 to about 500 F., at a superatmospheric pressure sutiicient to maintain substantially liquid phase conditions and with solvent compositions containing from about 1% to about 36% by weight of dissolved arylated carbohydrate. j v a a The arylglucitols which in the form of their aqueous solutions provide the present extractive solvent composi-' tions, may be prepared by synthetic means involving the condensation of a carbohydrate with an aromatichydro A R-c-R' Ba i-on),

in which each of A and B is a member of the group consisting of hydrogen and HzCOH, n is an integer from .1 to 4, R represents a member of the group consisting of aryl and alkylaryl in which aryl and alkylaryl represent aromatic hydrocarbon monovalent radicals or substituted derivatives thereof such as phenyl, tolyl, hydroxyphenyl, salicyl, etc. and R is a radical selected fromvhydrogen, aryl and alkylaryl. Details of the process of preparation and the preferred glucitol component ofthepresent solv ent composition will be set forth 'in thefollowing description thereof and in the examples herein provided; 1

Suitable aromatic hydrocarbons utilizable as starting materials in the preparation of the aryldesoxyglucit ol of the solvent composition include such monocyclic aromatic compounds as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5 trimethylbenzene (mesitylene) orthoethyltoluene, meta-ethyltoluene, p-ethyltoluene, n propylbenzene, isopropylbenzene or cumene, etc. Of these, benzene contains an aryl group and the others contain an alkylaryl group which groups become attached to the carbohydrate molecule ,during the alkylation process to form the present mono,- and di-aryldesoxyglucitols, Higher molecular weight alkylaromatic hydrocarbons are also suitable as the acceptors of the carbohydrate al'-' kylating agent, such as those produced by the alkylation of aromatic hydrocarbons witholefins and olefin polymers, The latter products which may contain alkyl groups containing, generally up to not morepthan abputlti carbon atoms, include, among others, such hydrocarbons as hexylbenzene, hexyltoluene, nonylbenzena: nonyltolugnel dodecylbenzene, dodecyltoluene, etc. Other suitable aromatic hydrocarbons utilizable as the aromatic reactant in the condensation thereof with a carbohydrate include as naphthalene, anthracene, phenanthrene, naphthacene, rubrene, etc.

Suitable carbohydrates which condense with the aromatic hydrocarbon in the method of synthesizing the present gluci tol solvent component include the simple sugars, their desoxy and omega carboxy derivatives, compound sugars or oligosaccharides, and the polysaccharides. Simple sugars include dioses, trioses, tetroses, pentoses, hexoses, heptoses, ocyoses, nonoses, and decoses. Compound sugars include disaccharides, trisaccharides, and tetrasaccharides. Polysaccharides include polysaccharides composed of only one type of sugar residue, polysaccharides composed of more than one type of sugar unit, polysaccharides composed of one type of uronic acid unit, i. e., polyuronides, polysaccharides composed of aldose (pentose or'hexose) and uronic acid units, polysaccharides containing hexose units esterified with an inorganic acid, and polysaccharides containing multiple identical sugar units. 7

Utilizable simple sugars include the diose: glycolaldehyde; tr-loses, such as glyceraldehyde and s-dihydroxy acetone; t etroses, such as erythrose, threose, erythrulose, and apio se; the pentoses such as arabinose, Xylose, ribose, lyxose, rhamnose (a desoxyhexose), fucose (a desoxyhexose), rhodeose, digitalose, and ketoxylose; the hexoses, such as mannose, glucose, idose, gulose, galactose, talose, allose, altrose, fructose, sorbose, tagatose, and psicose; heptoses such as glucoheptulose, and perseulose; octoses such as glucooctose, mannooctose, and galactooctose; nonoses such as glucononose, and mannononose; and decoses such as glucodecose. Desoxy derivatives of simple sugars are formed by the replacement of an hydroxyl substituent in a sugar with hydrogen, thereby forming a methyl or methylene linkage. The desoXypentoses and desoxyhexoses are the most commonly occurring of such compounds. The omega-carboxy derivatives of simple sugars, which are suitable in the process of the present invention include tartronic semi-aldehyde or its tautomer, hydroxypyruvic acid, a,'y-dihydroxyacetoacetic acid, threuronic acid, 4-keto-2,3,5-trihydroxypentanoic acid, xyluronic acid, S-keto-hexanoic acids such as 5-keto-al1onic acid, S-keto-gluconic acid, S-keto-mannonic acid, S-keto-gulonic acid, and S-keto-gallactonic acid, uronic acids such as glycouronic acid, mannuronic acid and gallacturonic acid, and the '6-keto-heptanoic acids. The simple sugars and their omega-carboxy derivatives, as starting materials for the process of this invention, may be represented by the following general formula:

in which A is selected from hydrogen and CHzOH, n is an integer having a value from 1 to about 12, and B is selected from hydrogen, CHzOH, and COOH. Thus, when A and B are hydrogen and n is equal to l, the compound then represented is glycolaldehyde; when A=H, n=1, and B=CH2OH, the compound is glyceraldehyde; when A=H, n=1, and B=COOH, the compound is tartaronic semialdehyde; when A=CH2OH, n=1, and B=H, the compound is s-dihydroxyacetone; etc.

Ketose sugars which may be used in the condensation type reaction with aromatic hydrocarbons of the aforementioned character to produce mono or diaryldesoXy ketitols useful in the formulation of the present solvent composition are monosaccharides and according to their chemical structure are hydroxy ketones, being referred to as trioses, tetroses, pentoses, hexoses, heptoses, and the like, depending upon the number of oxygen atoms present in their structure. These ketoses have the general formula: CnHZnOn in which it generally has a value of from 3 to about 8. Thus, these ketoses can all be regarded as polymers of formaldehyde (CH2O)1L. The diarylated ketoses or diaryldesoxy-ketitols may also be prepared from aromatic hydrocarbons and polysaccharides which yield ketose units on hydrolysis. Such polysaccharides include sucrose, inulin, puranose, raffinose, gentianose, melezitose, sta'chyose, and berbascose.

The utilizable oligosaccharides or compound sugars include disaccharides such as the pentose-hexose saccharides, including glucoapiose, vicianose, and primeverose; the methylpentose-hexose saccharides including glycorhamnoside, and rutinose; and the dihexoses such as turanose, maltose, lactose, cellobiose, gentiobiose, melibiose, sucrose, and trehalose. Other compound sugars are represented by the trisaccharides such as the methylpentoseheXose saccharides, including rhamninose, and robinose; the trihexoes saccharides such as mannotriose; and the trihexoses including rafiinose, melezitose, and gentianose. An example of a suitable tetrasaccharide is stachyose.

Various polysaccharides may also be alkylated with an aromatic hydrocarbon to produce glucitols useful as solvent components in the process of the present invention. These polysaccharides include pentosans such as araban, methylpentosans such as fugosan, the hexosans, such as starch, cellulose, glycogen, inulin, mannan, galactan, lichenin, levan, deXtran, and laminarin. All of the above polysaccharides are composed of one type of sugar residue. Other polysaccharides which are composed ofmore than one type of sugar unit such as the pentosans, like araboXylan and the hexosans like galactomannan may be used. .Other utilizable polysaccharides are represented by those composed of uronic acid units such as pectic acid and alginic acid; those composed of aldose (pentose or hexose) and uronic acid units such as gum arabic, damson gum, gum tragacanth, linseed mucilage, pectins, and those containing hexose units esterified with an inorganic acid such as certain seaweed polysaccharides like agar.

The acid-type alkylation catalyst which is specified for effecting the condensation between the aromatic hydrocarbon and the carbohydrate is preferably substantially anhydrous hydrogen fluoride, although hydrofluoric acid containing up to about 29% by weight of water may also be utilized as catalyst. The hydrogen fluoride may also be further diluted with various inert diluents when it is desirable to effect the alkylation with low hydrogen fluoride concentrations on an anhydrous basis. Suitable inert diluents include perfluoro derivatives of paraffinic hydrocarbons such as perfluoropropane, perfluoro-n-butane, perfluoro-n-pentane, perfluoro-n-he'xane, etc.

Although strong hydrofluoric acid is generally the catalyst preferred for use in producing di(alkylaryl)- and diaryl-desoxy-glucitols, certain Friedel-Crafts type catalysts, are also useful for this purpose. Thus, aluminum chloride, may be employed to catalyze the condensation reaction.

The alkylation or condensation of the aforementioned carbohydrates with the aromatic hydrocarbons described above to form the desoxyglucitol component of the present solvent composition may be carried out by reacting the aromatic hydrocarbon with the carbohydrate or related substance in the presence of hydrogen fluoride or other acid-type catalyst, and generally at temperatures of from about l0 to about +50 C. The pressure at which the reaction is carried out will vary with the reaction temperature used, the molar ratio of reactants and hydrogen fluoride catalyst present, and the volume of the particular reactor utilized. While many of the condensation reactions may be carried out at substantially atmospheric pressure, it may be desirable in certain instances and with certain reactants to carry out the reaction at pressures up to atmospheres or more. It is convenient get-acct i v in most instances to operate the equipment utilized at the pressure generated by the reaction mixture and the catalyst contained therein. The reaction is conveniently effected by slowly adding the hydrogen fluoride catalyst to a stirred mixture of the aromatic hydrocarbon and carbohydrate, or the reverse procedure may be followed by adding a mixture of the aromatic hydrocarbon and carbohydrate to the hydrogen fluoride catalyst with adequate agitation while the reaction temperature is maintained at from about 40 to about 100 C. by suitable cooling and/or heating means. It is often advisable or desirable to commingle the reactants and the catalyst at a relatively low temperature such as from about -80 to about -30 C,

and then permit the reaction mixture to warm gradually while the reactants and catalysts are stirred by suitable means, such as a motor-driven stirrer or other adequate mixing equipment. After the reaction has reached the desired degreeof completion, the hydrogen fluoride catalyst is removed from the reaction mixture by distillation at atmospheric or lower pressure or by passing an inert gas through the reaction mixture while maintaining it at a relatively low temperature. Also, the entire reaction mixture and catalyst may be mixed with water or may be .added to ice in order to quench the activity of the hydrogen fluoride catalyst and permit separation of the organic reaction products and unreacted starting matetrials from the catalyst. The organic reaction products may also be separated from the resulting aqueous hydrogen fluoride formed by dilution of the reaction mixture with water by means of an organic solvent such as ether in which all or some of the organic material may be dissolved. Thus, the product formed by reacting toluene with glucose or cellulose in the presence of substantially anhydrous hydrogen fluoride at 30 C. is separated into an ether-soluble and water-insoluble product, and an ether-insoluble and water-soluble product.

The ratio of aromatic hydrocarbon to carbohydrate charged to the condensation reaction is generally equimolar, although this ratio may vary from 0.1 to l to to 1, if desired, ratios greater than 1 to 1 increasing the yield of diaryl carbohydrate condensation product.

The above discussed catalyzed reaction between carbohydrates and aromatic compounds canbe extended to include, on the one hand, aromatic derivatives, included within the scope of the term aryl and alkylaryl as} utilized herein, such as phenol, chlorobenzene, anisole, benzoic acid, sa-licyclic acid, and the like, and on the other hand, carbohydrate derivatives such as glucuronolactone, etc., the only limitation here being that a potentially free aldehyde or ketone group be present in the carbohydrate derivative. For example, the catalyzed interaction of glucose and toluene gives, among other products, pure organic materials having the following structures:

CH; C

The catalyzed interaction of glucose and phenol gives,

ing structures: 1

amongothers, pure reaction products having the follow H H E O O O l i H( JOH HC EOH HOCH HO H HAJOH HGOH H OH H HIOH 3H2OH The catalyzed interaction of ethylbenzene and glucose gives, among others, reaction products having the following structures:

-CHaOIEl $2 5 $2 5 CrHs l3 HC IOH HJJOH HO OH HO JH 0 HO OH H OH H on CHiOH IH2OH The catalyzed interaction of fructose and toluene gives, among others, pure reaction products having the following structures:

The catalyzed interaction of glucose and chlorobenzene gives, among others, pure reaction products having the following structures:

"The catalyzed interaction of glucuronolactone with benzene gives, among others, reaction products having the following structures:

The above compounds may be obtained as pure crystalline materials in good yields as products of the appropriate reactions and each may be utilized in the form of its aqueous solution as the solvent composition herein. In some cases the raw products consist of mixtures of compounds which may require extraction or suitable chemical treatment for recovery of a particular component which may be more desirable than other components of the mixed product.

The extractive solvents herein provided for the recovery of aromatic hydrocarbons from hydrocarbon mixtures of the same with non-aromatic hydrocarbons are aqueous solutions of the above arylated carbohydrates, also referred to as aryldesoxyglucitols, said solution containing from about 1% to about 30% of the latter solute, depending upon the desired solubility of the aromatic hydrocarbon in the solvent. These solvent extractants are generally prepared merely by dissolving the arylated carbohydrate in water, in the case of certain high molecular weight aromatic alkylates of carbohydrates or when 2 or more molecules of aromatic hydrocarbon are condensed with each molecule of carbohydrate, certain organic compounds such as the alcohols, ketones and other readily water-soluble organic compounds may be added to the aqueous solution to enhance the solubility of the arylated carbohydrate in the aqueous solution. The preferred solvent compositions for extraction of aromatic hydrocarbons from hydrocarbon mixtures contain at least 5%, generally up to about 20% by weight of the arylated carbohydrate, the resulting solutions having the desirable viscosity and boiling point characteristics particularly suitable for solvent extraction in the present process.

Hydrocarbon mixtures which may be employed as feed stocks in extraction processes utilizing the present solvent composition contain one or more aromatic hydrocarbons in admixture-with olefinic, naphthenic or paraifinic hydrocarbons capable of being maintained in substantially liquid phase condition at the temperature and pressure at which the extraction process is-to be operated. The prescut solvent extraction process is particularly applicable to the separation of hydrocarbon mixtures, the individual components of which boil at or near the same temperature, making separation by simple or fractional distillation a difiicult method of separation because of azeotrope formation. Thus, normally liquid hydrocarbon mixtures boiling from about 70 to about C. and containing benzene and toluene as the aromatic components, n-hexane, cyclohexane, the various branched-chain aliphatic hexanes, the hexenes, the C1 olefins, paraflins and naphthenes and usually smaller quantities of the C5 and Ca hydrocarbons constitutes a typical charging stock fractionated from petroleum or its conversion products which may be utilized as a feed stock in the present process. Other hydrocarbon mixtures may be selected from the higher boiling fractions of petroleum or petroleum conversion products, including such fractions which contain bicyclic and polycyclic aromatic components therein, such as naphthalene, the monoand polyalkyl-substituted naphthalenes, such as dimethyl naphthalene, phenanthrene, anthracene and others, as well as the monoand polyalkyl substituted derivatives and the higher homologs or the alkyl benzene series. As indicated hereinabove, the present solvent extractant process is particularly applicable to the separation of hydrocarbon mixtures which cannot be conveniently or are impossible to separate by other conventional, simpler methods, such as fractional distillation.

The preferred method for effecting solvent extraction of an aromatic hydrocarbon containing hydrocarbon mixture comprises countercurrent liquid-liquid phase solvent extraction in which the present solvent, usually the phase of greatest density, is introduced into the upper portion of the liquid-liquid contacting column and allowed to flow downwardly through a packing material or other liquid-liquid contacting means such as bubble caps and trays, against a rising stream of liquid hydrocarbon charge stock admitted into the lower portion of the extraction zone. The aqueous solvent phase becomes progressively richer in the soluble aromatic component of the feed stock mixture as it flows downwardly through the extraction zone and is ultimately withdrawn from the lower portion of the extraction zone as a fat solvent stream containing the aromatic hydrocarbon extracted from the feed stock mixture. A raflinate phase lean in aromatic hydrocarbons or substantially stripped thereof is discharged from the top of the extraction zone and removed from the process flow.

Generally, substantially complete recovery of the aromatic component of the feed stock mixture is obtained when utilizing solvent to feed stock ratios of from about 1 to 1 to about 12 to 1 volumes of aqueous solvent per volume of feed stock, although higher ratios may be employed, when desired. The extraction is generally effected at a superatmospheric pressure sufiicient to maintain the solvent and feed stock mixture in substantially liquid phase at temperatures of from 50 to about 200 C., at which temperatures the extraction may be efiected. The particular choice of temperature and pressure conditions to be maintained within the extraction zone depends upon the character, and particularly the boiling range of the feed stock mixture and is determined by trial methods for the particular feed stock under consideration.

The solvent composition, containing the arylated carbohydrate, is under certain conditions of temperature and exposure to air, subject to oxidative deterioration, causing the formation of acidic materials which may be corrosive to the steel equipment utilized in the extraction process. In order to inhibit such oxidative deterioration, the solvent composition may contain an amino compound or phenolic material which inhibits oxidation, including such compounds as the alkylphenols, particularly the -tert-valkyl-substituted phenols, such as di-tert-butylphenol, tert-butylhydroxyanisole, an amine such as phenylenediamine, N,N.'-di-sec-butylphenylenediamine, an amino-phenol, such as 2-tert-butyl-4-aminophenol, etc. The oxidation inhibitor, when utilized in the present solvent composition, is preferably added to the aqueous arylated carbohydrate in an amount of from about 0.01 to about 5% and preferably from about 0.1 to about 2% by weight of the aqueous mixture.

The extracted aromatic hydrocarbon present in the fat solvent stream removed from the bottom of the extraction zone may be recovered therefrom by any of a number of alternative procedures, including the addition of water to the fat solvent to thereby reduce the solubility of the aromatic hydrocarbon in the solvent composition, by reducing the temperature of the fat solvent stream, thereby reducing the solubility of the aromatic hydrocarbon in the fat solvent, by countercurrent extraction of the fat solvent with another solvent for the aromatic component, or preferably, by distilling the aromatic hydrocarbon from the fat solvent in a so-called stripping operation wherein the pressure is reduced on the fat solvent stream removed from the extraction zone to thereby distill the aromatic solute therefrom or merely by heating the fat solvent to a temperature exceeding the boiling point of the aromatic in the fat solvent. In actual commercial usage, a combination of pressure reduction and reboiling is utilized, the fat solvent stream at the elevated temperature and pressure existing within the extraction zone being introduced into the upper portion of a stripping zone wherein the pressure is reduced below the level existing in the extraction zone, thereby flashing the aromatic hydrocarbon solute, together with a portion of the water, from the aqueous solvent and thereafter successively reducing the pressure on the fat solvent to atmospheric and heating the residue to distill therefrom the remaining trace of aromatic solute, usually with the aid of heat supplied to the reboiling section of such a stripping column. The fat solvent residue from which the aromatic hydrocarbon solute has been vaporized, and referred to as the lean solvent, may be recycled directly or after addition of water thereto to reconstitute the solvent to its original composition, to the extraction zone for use therein.

The present invention is further illustrated with respect to several of its embodiments in the following examples, which, however, are intended merely as exemplary runs which demonstrate the feasibility and operability of the present method of extraction and are in no way intended as limits on the generally broad scope of the invention.

Example I Benzene is soluble in superheated water to the extent of 0.7 volume per 100 volumes of water at 157 C. and to the extent of 5.0 volumes per 100 volumes of water at 239 C., the solubility being determined in a Magne Dash autoclave heated to the above temperatures and the mixture slowly agitated at said temperatures. The solubility of benzene in water may be increased to 1.6 volumes per 100 volumes per 100 volumes at 157 C. and to 8.4 volumes per 100 volumes at 239 C. by dissolving an arylated carbohydrate in the water to provide a solution containing by weight of the arylated carbohydrate. The arylated carbohydrate utilized in the latter solubility run was a mono-orthoxylene alkylate of fructose which melted at 137 C. and it has the followt 10 this product being prepared by the hydro catalyzed reaction of ortho-xylene with fructose. The above-indicated compound increased the solubility of toluene in water from 2.2 volumes per volumesof solvent at 153 C. to 10.2 volumes per 100 volumes per solvent. I

Example II Example III A synthetic hydrocarbon mixture prepared by mixing 10 weight proportions of n-pentane, 10 weight proportions of cyclopentane, 25 parts by weight of n-hexane, 15 parts by weight of 2,3-dimethylbutane and 40 parts byv weight of toluene is utilized as feed stock into a counter-. current solvent extraction column comprising a'vertical pipe packed with Berl saddles and containing approximately 12 theoretical plates, the feed stock being introduced into or onto a plate approximately 7 theoretical plates from the top of the column. The solvent composition consists of an aqueous solution of a glucose alkylate of toluene containing 1 tolyl nucleus per glucose residue, synthesized by thehydnogen fluoride catalyzed alkylation of glucose with toluene. The aqueous solution of solvent-extractant containing 18% by weight of the toluene-glucose alkylate, is charged into the extraction column onto the top plate thereof at a rate suflicient to provide a solvent to feed stock ratio of 10 to 1 volumes of solvent per vlume of feed stock. The solvent composition also contains approximately 0.12% of diethanolamine, added thereto as an oxidation inhibitor to retard deterioration of the glucose-toluene alkylate as evidenced by tar and acid formation, thereby preventing the development of acidic corrosion materials in the solvent composition if air is accidently contacted with the aqueous solvent composition during the extraction process. A reflux stream which is recovered from the flash section of the stripping column, as hereinafter described, is charged into the extraction column onto approximately the bottom plate thereof at a rate equivalent of 20 to 1 volumes of solvent per volume of reflux. Each of the feed stock, reflux and solvent composition streams charged into the extraction column are preheated to C. at p. s. i. g. pressure.

A raflinate stream of the feed stock is removed from the top of the extraction column and upon analysis consists of paraflins and naphthenes with less than 0.12% of toluene contained therein.

A fat solvent stream is removed from the bottom of the extraction column and pumped into a stripping column comprising a flash section wherein the pressure on the fat solvent is reduced in 3 successive stages from 150 p. s. i. g. to atmospheric pressure, the stripping column also containing a fractionating section below the flash chamber and a reboiler coil in the lower portion of the column wherein the fat solvent bottoms are boiled to produce steam which effects the desired stripping action on the fat solvent. An overhead stream from the stripping column, the non-aqueous portion of which upon analysis comprises 30% by weight of normal pentane, 19% by weight of cyclopentane, 4% by weight of normal hexane and 47% by weight of toluene, is continuously removed from the stripping column and recycled to the bottom of the extractor as the aforementioned reflux stream to displace higher boiling paraflin hydrocarbons from the fat solvent stream just prior to removal of the latter from the extraction column, the displaced higher at rate l1 boiling paraflins comprising the raflinate stream leaving the top of the'extraction column.

Aside-cut fraction is removed from approximately the mid-portion of the stripping column, the non-aqueous portion of which consists of 99.9% toluene. The aqueous layers accumulating in the overhead and side-cut receivers are combined and charged as superheated steam into the lower portion of the stripping column immediately above the reboiler coils.

A lean solvent residue is removed from the bottom of the stripper at approximately 130 C. and pumped at the ambient pressure existing in the extraction column, that is, at 150 p. s. i. g., into the solvent inlet line leading into the 'top of the extraction column wherein it is employed as the solvent composition in the latter column. This stream reconstituted to its 18% by volume of glucose-toluene alkylate composition and 0.1% by weight of diethanolamine oxidation inhibitor concentration maintains this composition throughout an extended period of recycle in the successive, continuous extractionstripping stages hereinabove described. Periodically, a small proportion of the total solvent inventory is removed from the recycle stream and previously made-up solvent composition added thereto for replacement of the removed portion.

The net product of the process, that is, the side-cut of the stripping column consisting of 99.9% toluene, is recovered at a rate equivalent to 98% of the total toluene charged into the process as feed stock and may be claytreated to remove the extremely small amount of impurities present in the side-cut fraction.

We claim as our invention:

1. A. method of separating an aromatic hydrocarbon from a hydrocarbon mixture containing the same which comprises contacting said hydrocarbon mixture with an aqueous solution of an aryl-desoxyglucitol to form a rich solvent phase comprising said aromatic hydrocarbon dissolved in said aqueous solution and a raflinate phase 12 comprising the non-aromatic components of said hydrocarbon mixture, separating said rich solvent phase from said rafiinate phase, and removing and recovering the dissolved aromatic hydrocarbon from said rich solvent phase.

2. The process of claim 1 further characterized in that hydrocarbon mixture is contacted with said aqueous solution at a temperature above about C. and at a pressure sufiicient to maintain said aqueous solution and said mixture in substantially liquid phase.

3. The process of claim 1 further characterized in that said aqueous solution contains at least 1% by weight of said aryl-desoxyglucitol.

4. The process of claim 3 further characterized in that said aqueous solution contains from about 5% to about 25% by weight of said aryl-desoxyglucitol.

5. The process of claim 1 further characterized in that said aryl-desoxyglucitol is an alkylate product of a hex-ose sugar carbohydrate and an aromatic hydrocarbon.

6. The process of claim 5 further characterized in that the last-mentioned aromatic hydrocarbon is a monocyclic aromatic hydrocarbon.

7. The process of claim 6 further characterized in that said monocyclic aromatic hydrocarbon is benzene.

8. The process of claim 6 further characterized in that said monocyclic aromatic hydrocarbon is toluene.

9. The process of claim 6 further characterized in that said monocyclic aromatic hydrocarbon is xylene.

10. The process of claim 6 further characterized in that said carbohydrate is glucose.

OTHER REFERENCES Pigman et al.: Chemistry of Carbohydrates, Academic Press, Inc., New York, New York (1948), pages -7. 

1. A METHOD OF SEPARATING AN AROMATIC HYDROCARBON FROM A HYDROCARBON MIXTURE CONTAINING THE SAME WHICH COMPRISES CONTACTING SAID HYDROCARBON MIXTURE WITH AN AQUEOUS SOLUTION OF AN ARYL-DESOXGLUCITOL TO FORM A RICH SOLVENT PHASE COMPRISING SAID AROMATIC HYDROCARBON DISSOLVED IN SAID AQUEOUS SOLUTION AND RAFFINATE PHASE COMPRISING THE NON-AROMATIC COMPONENTS OF SAID HYDROCARBON MIXTURE, SEPARATING SAID RICH SOLVENT PHASE FROM SAID RAFFINATE PHASE, AND REMOVING AND RECOVERING THE DISSOLVED AROMATIC HYDROCARBON FROM SAID RICH SOLVENT PHASE. 